Material for photovoltaic film, solar cell, process for producing photovoltaic film material and process for producing photovoltaic film

ABSTRACT

To provide, in relation to a dye-sensitized solar cell, an inexpensive photovoltaic film material which can solve problems arising from usage of a sensitizing dye comprising an organic substance; and a solar cell having the photovoltaic film.  
     A photovoltaic film  30  comprises photocatalyst-coated particles which include inorganic material particles, titanium dioxide particles coated on the surface of the inorganic material particles, and lithium particles attached to the inorganic material particles and/or the titanium dioxide particles. The photocatalyst-coated particles are obtained by means of: producing a mixture in which an aqueous solution obtained by means of mixing titanium hydroxide gel and aqueous hydrogen peroxide, powder consisting of the inorganic material particles, and water; leaving to stand a second mixture obtained by means of mixing the mixture and lithium chloride aqueous solution, thereby obtaining a product material in which titanium hydroxide is coated on the surface of the inorganic material particles; and thereafter baking the product material. The photocatalyst-coated particles are formed into paste with the use of a binder, and coated onto a conductive glass plate, to thus form a coating.

TECHNICAL FIELD

The present invention relates to a photovoltaic film in a thin filmsolar cell, the photovoltaic film for generating excitation energy, andto a method for manufacturing the same; as well as to a photovoltaicfilm material and a solar cell having the photovoltaic film.

BACKGROUND ART

In 1991, Graetzel, et al, reported a “dye-sensitized solar cell” (alsocalled a photoelectrochemical cell, a Graetzel solar cell, or the like).In contrast to a silicon solar cell, the solar cell does not employ asilicon semiconductor, has an electrochemical-cell structure with aniodine solution interposed between cells, and employs materials whichare inexpensive, as well as easy to fabricate; accordingly, the solarcell is expected to allow production at low cost.

A dye-sensitized solar cell comprises an electrode obtained by means ofbaking titanium dioxide particles onto a transparent conductive glassplate and causing an organic sensitizing dye, such as a rutheniumcomplex, to be absorbed; and a counter electrode of an identicalconductive glass plate; and is configured such that a gap between theelectrodes is filled with an electrolyte solution.

In a specific example, a dye-sensitized solar cell B, which isconfigured as shown in FIG. 1, comprises a pair of conductive glassplates 10 and 20, a photovoltaic film 30′ disposed on the conductiveglass plate 10, and an electrolyte layer 40. The conductive glass plate10 is configured such that a conductive film is formed on a tabularglass, the conductive film being formed on the photovoltaic film 30′side. Similarly, the conductive glass plate 20 is also configured suchthat a conductive film is formed on a tabular glass, the conductive filmbeing formed on the electrolyte layer 40 side. Meanwhile, as describedabove, the photovoltaic film 30′ comprises titanium dioxide particles onwhich an organic sensitizing dye is absorbed. The photovoltaic film 30′serves as a photovoltaic film for generating excitation energy.Meanwhile, the electrolyte layer 40 is in such a state that anelectrolyte solution is filled therein with the conductive glass plate20 and a spacer therebetween.

A power generation mechanism in a dye-sensitized solar cell is initiatedfrom, at first, entry of the photovoltaic film 30′ into a state inwhich, upon absorption of light energy, the sensitizing dye is excited.Next, the excitation energy of the sensitizing dye is transmitted totitanium dioxide particles in the form of electrons, thereby furtherreaching the conductive glass plate 10 and shifting to the conductiveglass plate 20 on a counter electrode. The mechanism allows delivery ofelectric power at this time. The electrons, which have transited to thecounter electrode, subsequently return to the sensitizing dye or to thetitanium dioxide particles by way of a redox reaction in the electrolytesolution. It can be said that an electromotive force is obtained throughrepetition of this cycle.

This solar cell is characterized in that titanium dioxide, which itselfcan utilize only energy in the ultraviolet range, is supplemented andenhanced by means of addition of the sensitizing dye.

Meanwhile, the configuration of a solar cell is not limited to theconfiguration shown in FIG. 1; for instance, there is sometimes employedsuch a configuration that the electrolyte layer 40 is omitted, thephotovoltaic film 30′ and the conductive glass plate 20 are brought intocontact, and the photovoltaic film 30′ is impregnated with anelectrolyte solution.

In addition, in the conventional solar cell, in order to form aphotovoltaic film on a conductive glass plate, usually, baking operationhas been performed after a conductive glass plate is coated with pasteof a photovoltaic film. More specifically, baking operation has beenperformed for forming passages between titanium dioxide particles, aswell as for fixing the photovoltaic film onto the conductive glassplate.

However, the dye-sensitized solar cell devised by Graetzel employs asensitizing dye, such as RuL2(NCS)2 #L=4,4′-dicarboxy-2,2′bipyridine,[Ru(dcbpy)2 (NCS)2]·2H2O #dcbpy=2,2′-bipyridyl-4,4′-dicalboxylic acid,each of which is a ruthenium complex. These sensitizing dyes, which areextremely expensive, pose a bottleneck in mass production andindustrialization from the viewpoint of cost.

In addition, a problem arising from usage of a sensitizing dyeconstituted of an organic substance is also present. More specifically,since a sensitizing dye constituted of an organic substance is used, aproblem arises in view of a useful life and light resistance of thesensitizing dye. Meanwhile, presence of moisture is known to causediscoloration of a sensitizing dye.

To this end, the present invention aims at providing an inexpensivephotovoltaic film material which can solve the problem—arising fromusage of a sensitizing dye constituted of an organic substance—, a solarcell having the photovoltaic film, and, furthermore, a method formanufacturing the same.

DISCLOSURE OF THE INVENTION

The present invention has been conceived to solve the above problem. Afirst aspect of the invention provides a photovoltaic film material, foruse in a photovoltaic film to be disposed in a solar cell, characterizedby having photocatalyst-coated particles including: inorganic materialparticles which are particles of an inorganic material; photocatalystparticles coated on the surface of the inorganic material particles; andlithium particles attached onto the inorganic material particles and/orthe photocatalyst particles.

The photovoltaic film material of the first aspect produces a paste-likephotovoltaic film material by making use of a binder; and the paste-likephotovoltaic film material is coated on a conductive film, such as thatdisposed on a conductive glass plate; that is, a conductive film servingas an electrode, thereby forming a photovoltaic film. Meanwhile, thephotovoltaic film material coated on the conductive film may be baked.While in a state of a photovoltaic film, the inorganic materialparticles function as a sensitizing dye. Energy excited in the inorganicmaterial particles is transmitted to the photocatalyst particles in theform of electrons. The electrons are sequentially transmitted from onephotocatalyst particle to another, thereby reaching the conductive film,to thus generate an electromotive force. In addition, since thephotovoltaic film material includes the lithium particles, the presenceof the lithium particles enables to maintain the electromotive forceeven under a light-shielded condition. According to the photovoltaicfilm material of the first aspect, since inorganic material particlesare adopted, an inexpensive material, such as red iron oxide, can beemployed, thereby enabling manufacture of a photovoltaic film at lowcost. In addition, since an organic substance is not employed in thephotovoltaic film material, problems arising from employment of asensitizing dye constituted of an organic substance (e.g., problems withregard to a useful life and light resistance of the sensitizing dye, anda problem of discoloration of a sensitizing dye caused by moisture) willbe prevented. Furthermore, since the only requirements are to form thephotovoltaic film material of the invention into paste and to coat thesame on a conductive film, a baking step can be omitted from formationof a photovoltaic film, thereby enabling reduction of manufacturing costalso in this regard.

Meanwhile, the first aspect of the invention may alternatively bedefined as providing “a photovoltaic film material, for use in aphotovoltaic film to be disposed on a solar cell, characterized byhaving photocatalyst-coated particles including: inorganic materialparticles which are particles of an inorganic material; andphotocatalyst particles coated on the surface of the inorganic materialparticles.”

A second aspect is characterized in that, in the first aspect, thephotocatalyst-coated particles are obtained by means of producing amixture in which an aqueous solution obtained by means of mixingtitanium hydroxide gel and aqueous hydrogen peroxide, powder consistingof the inorganic material particles, and water are mixed (alternatively,may have been mixed in advance); leaving to stand a second mixtureobtained by means of mixing the mixture, and lithium chloride or alithium chloride aqueous solution, thereby forming a product material inwhich titanium hydroxide is coated on at least the surface of theinorganic material particles; and thereafter baking the productmaterial. The baking temperature in this case is preferably set to 200°C. or higher.

A third aspect is characterized in that, in the first or second aspect,the inorganic material which constitutes the inorganic materialparticles is an inorganic pigment or a metal oxide. Meanwhile, the thirdaspect may alternatively be defined as “being characterized in that, inthe first or second aspect, the inorganic material particles areinorganic pigment particles (may alternatively be referred to asinorganic dye particles) or metal oxide particles.” Alternatively, thethird aspect may be defined as “being characterized in that theinorganic material particles in the first or second aspect are particlesof a metal oxide, such as red iron oxide, yellow iron oxide, or blackiron oxide.”

A fourth aspect is characterized in that, in any one of the first tothird aspects, the photocatalyst particles are titanium dioxideparticles.

A fifth aspect is characterized in that, in any one of the first tofourth aspects, the photovoltaic film material further includes abinder, and in that the photovoltaic film material is formed into acoating fluid. By virtue thereof, by means of merely coating thephotovoltaic film material on a conductive film, the photovoltaic filmcan be formed on a solar cell.

A sixth aspect is characterized in that, in any one of the first tofifth aspects, the binder is any one of: an aqueous solution obtained bymeans of mixing titanium hydroxide gel and aqueous hydrogen peroxide; amixture of an aqueous solution obtained by means of mixing titaniumhydroxide gel and aqueous hydrogen peroxide, and a lithium silicateaqueous solution; and lithium silicate.

Meanwhile, the sixth aspect may alternatively be defined as “beingcharacterized in that, in any one of the first to fifth aspects, thebinder is an aqueous solution obtained by means of mixing titaniumhydroxide gel and aqueous hydrogen peroxide; or a mixture of an aqueoussolution obtained by means of mixing titanium hydroxide gel and aqueoushydrogen peroxide, and a lithium silicate aqueous solution; or lithiumsilicate.”

A seventh aspect provides a solar cell including a photovoltaic film,characterized in that the photovoltaic film has photocatalyst-coatedparticles including: inorganic material particles which are particles ofan inorganic material; photocatalyst particles which are coated on thesurface of the inorganic material particles; and lithium particlesattached onto the inorganic material particles and/or the photocatalystparticles.

In a solar cell of the seventh aspect, in the photovoltaic film, theinorganic material particles function as a sensitizing dye. Energyexcited in the inorganic material particles is transmitted to thephotocatalyst particles in the form of electrons; and the electrons aresequentially transmitted from one photocatalyst particle to another,thereby reaching a conductive film (e.g., a conductive film disposed ona conductive glass plate) with which the photovoltaic film is incontact, to thus generate an electromotive force. In addition, since thephotovoltaic film material includes the lithium particles, the presenceof the lithium particles enables maintenance of the electromotive forceeven under a light-shielded condition. According to the solar cell ofthe seventh aspect, since inorganic material particles are employed inthe photovoltaic film, an inexpensive material, such as selenium red,can be employed, thereby enabling manufacture of a photovoltaic film atlow cost. In addition, since an organic substance is not employed in thephotovoltaic film, problems arising from employment of a sensitizing dyeconstituted of an organic substance (e.g., problems with regard to auseful life and light resistance of the sensitizing dye, and a problemof discoloration of a sensitizing dye caused by moisture) will beprevented.

Meanwhile, the seventh aspect may alternatively be defined as providing“a solar cell including a photovoltaic film, characterized in that thephotovoltaic film has photocatalyst-coated particles including:inorganic material particles which are photocatalyst-coated particlesand which are particles of an inorganic material; and photocatalystparticles coated on the surface of the inorganic material particles.”

An eighth aspect is characterized in that, in the seventh aspect, thephotocatalyst-coated particles are obtained by means of producing amixture in which an aqueous solution obtained by means of mixingtitanium hydroxide gel and aqueous hydrogen peroxide, powder consistingof the inorganic material particles, and water are mixed (alternatively,may have been mixed in advance); leaving to stand a second mixtureobtained by means of mixing the mixture, and lithium chloride or alithium chloride aqueous solution, thereby forming a product material inwhich titanium hydroxide is coated on at least the surface of theinorganic material particles; and thereafter baking the productmaterial. The baking temperature in this case is preferably set to 200°C. or higher.

A ninth aspect is characterized in that, in the seventh or eighthaspect, the photovoltaic film further includes titanium dioxide whichhas been transformed from titanium hydroxide by means of baking acoating-fluid-like product material obtained by means of kneading thephotocatalyst-coated particles in an aqueous solution having beenobtained by means of mixing titanium hydroxide gel and aqueous hydrogenperoxide. The baking temperature in this case is preferably set to 200°C. or higher.

A tenth aspect is characterized in that, in any one of the seventh toninth aspects, the inorganic material which constitutes the inorganicmaterial particles is an inorganic pigment or a metal oxide. Meanwhile,the tenth aspect may alternatively be defined as “being characterized inthat, in any one of the seventh to ninth aspects, the inorganic materialparticles are inorganic pigment particles or metal oxide particles.”

An eleventh aspect is characterized in that, in any one of the seventhto tenth aspects, the photovoltaic film further includes a binder.

A twelfth aspect is characterized in that, in the eleventh aspect, thebinder is any one of: an aqueous solution obtained by means of mixingtitanium hydroxide gel and aqueous hydrogen peroxide; a mixture of anaqueous solution obtained by means of mixing titanium hydroxide gel andaqueous hydrogen peroxide, and a lithium silicate aqueous solution; andlithium silicate.

Meanwhile, the twelfth aspect may alternatively be defined as “beingcharacterized in that, in the eleventh aspect, the binder is an aqueoussolution obtained by means of mixing titanium hydroxide gel and aqueoushydrogen peroxide; or a mixture of an aqueous solution obtained by meansof mixing titanium hydroxide gel and aqueous hydrogen peroxide, and alithium silicate aqueous solution; or lithium silicate.”

A thirteenth aspect provides a method for manufacturing a photovoltaicfilm material for use in a photovoltaic film to be disposed in a solarcell, characterized by including a first-mixture preparation step ofproducing a first mixture in which an aqueous solution obtained by meansof mixing titanium hydroxide gel and aqueous hydrogen peroxide, powderconsisting of inorganic material particles—which are particles of aninorganic material—and water are mixed (alternatively, may have beenmixed in advance); a second-mixture production step of producing asecond mixture by means of mixing lithium chloride or a lithium chlorideaqueous solution into the mixture produced in the first-mixturepreparation step; a production-material formation step of leaving tostand the second mixture produced in the second-mixture preparationstep, thereby forming a product material in which titanium hydroxide iscoated on at least the surface of the inorganic material particles; anda baking step of baking the product material formed in theproduct-material formation step, thereby producing a photovoltaic filmmaterial.

A photovoltaic film material manufactured in accordance with themanufacturing method of the thirteenth aspect comprises inorganicmaterial particles which are particles of an inorganic material;titanium dioxide particles which serve as photocatalyst particles coatedon the surface of the inorganic material particles; and lithiumparticles attached onto the inorganic material particles and/or thetitanium dioxide particles. By making use of a binder, the photovoltaicfilm material produces a coating-fluid-like photovoltaic film material;and the coating-fluid-like photovoltaic film material is coated on aconductive film (e.g., a conductive film disposed on a conductive glassplate), thereby forming a photovoltaic film. Meanwhile, the photovoltaicfilm material coated on the conductive film may be baked. While in astate of a photovoltaic film, the inorganic material particles functionas a sensitizing dye. Energy excited in the inorganic material particlesis transmitted to the photocatalyst particles in the form of electrons.The electrons are sequentially transmitted from one photocatalystparticle to another, thereby reaching the conductive film, to thusgenerate an electromotive force. In addition, since the photovoltaicfilm material includes the lithium particles, the presence of thelithium particles enables maintenance of the electromotive force evenunder a light-shielded condition. According to manufacturing method ofthe invention, since inorganic material particles are adopted, aninexpensive material, such as selenium red, can be employed, therebyenabling manufacture of a photovoltaic film at low cost. In addition,since an organic substance is not employed in the photovoltaic filmmaterial, problems arising from employment of a sensitizing dyeconstituted of an organic substance (e.g., problems with regard to auseful life and light resistance of the sensitizing dye, and a problemof discoloration of a sensitizing dye caused by moisture) will beprevented. Furthermore, since the only requirements are to form thephotovoltaic film material manufactured in accordance with themanufacturing method of the invention into coating fluid and to coat thesame on a conductive film, the baking step can be omitted from formationof a photovoltaic film, thereby enabling reduction of manufacturing costalso in this regard. In addition, the amount of titanium dioxideparticles coated on the surface of the inorganic material particles canbe adjusted by means of adjusting the concentration of the titaniumhydroxide sol in the aqueous solution during the mixture preparationstep. The baking temperature in the baking step is preferably set to200° C. or higher.

Meanwhile, the thirteenth aspect may alternatively be defined asproviding “a method for manufacturing a photovoltaic film material foruse in a photovoltaic film to be disposed in a solar cell, characterizedby including a first-mixture preparation step of producing a firstmixture in which an aqueous solution obtained by means of mixingtitanium hydroxide gel and aqueous hydrogen peroxide, powder consistingof inorganic material particles—which are particles of an inorganicmaterial—and water are mixed (alternatively, may have been mixed inadvance); a second-mixture production step of producing a second mixtureby means of mixing lithium chloride or a lithium chloride aqueoussolution into the mixture produced in the first-mixture preparationstep; a production-material formation step of leaving to stand thesecond mixture produced in the second-mixture preparation step, therebyforming a product material in which titanium hydroxide is coated on atleast the surface of the inorganic material particles; a drying step ofdrying the product material formed in the product-material formationstep; and a baking step of baking the product material dried in thedrying step, thereby producing a photovoltaic film material.”

Alternatively, the thirteenth aspect may be defined as providing “amethod for manufacturing a photovoltaic film material for use in aphotovoltaic film to be disposed in a solar cell, characterized byincluding a mixture preparation step of producing a first mixture inwhich an aqueous solution obtained by means of mixing titanium hydroxidegel and aqueous hydrogen peroxide, powder consisting of inorganicmaterial particles—which are particles of an inorganic material—andwater are mixed (alternatively, may have been mixed in advance); aproduction-material formation step of leaving to stand the mixtureproduced in the mixture preparation step, thereby forming a productmaterial in which titanium hydroxide is coated on the surface of theinorganic material particles; and a baking step of baking the productmaterial formed in the product-material formation step, therebyproducing a photovoltaic film material.”

Alternatively, the thirteenth aspect may be defined as providing “amethod for manufacturing a photovoltaic film material for use in aphotovoltaic film to be disposed in a solar cell, characterized byincluding a mixture preparation step of producing a first mixture inwhich an aqueous solution obtained by means of mixing titanium hydroxidegel and aqueous hydrogen peroxide, powder consisting of inorganicmaterial particles—which are particles of an inorganic material—andwater are mixed (alternatively, may have been mixed in advance); aproduction-material formation step of leaving to stand a mixtureproduced in the mixture preparation step, thereby forming a productmaterial in which titanium hydroxide is coated on the surface of theinorganic material particles; a drying step of drying the productmaterial produced in the product-material formation step; and a bakingstep of baking the product material dried in the drying step, therebyproducing photovoltaic film material.”

Also in the modifications of the thirteenth aspect, the bakingtemperature in the baking step is preferably set to 200° C. or higher.

A fourteenth aspect provides a method for manufacturing a photovoltaicfilm material for use in a photovoltaic film to be disposed in a solarcell, characterized by including: a production-material formation stepof producing a precipitated product material by means of producing anaqueous solution having titanium hydroxide, powder consisting ofinorganic material particles—which are particles of an inorganicmaterial—, and lithium chloride, and leaving the thus-produced aqueoussolution; and a baking step of baking the product material formed in theproduct-material formation step, thereby producing a photovoltaic filmmaterial.

A photovoltaic film material manufactured in accordance with themanufacturing method of the fourteenth aspect comprises inorganicmaterial particles which are particles of an inorganic material;titanium dioxide particles which serve as photocatalyst particles coatedon the surface of the inorganic material particles; and lithiumparticles attached onto the inorganic material particles and/or thetitanium dioxide particles. By making use of a binder, the photovoltaicfilm material produces a coating-fluid-like photovoltaic film material;and the coating-fluid-like photovoltaic film material is coated on aconductive film (e.g., a conductive film disposed on a conductive glassplate), thereby forming a photovoltaic film. Meanwhile, the photovoltaicfilm material coated on the conductive film may be baked. While in astate of a photovoltaic film, the inorganic material particles functionas a sensitizing dye. Energy excited in the inorganic material particlesis transmitted to the photocatalyst particles in the form of electrons.The electrons are sequentially transmitted from one photocatalystparticle to another, thereby reaching the conductive film, to thusgenerate an electromotive force. In addition, since the photovoltaicfilm material includes the lithium particles, the presence of thelithium particles enables maintenance of the electromotive force evenunder a light-shielded condition. According to manufacturing method ofthe invention, since inorganic material particles are adopted, aninexpensive material, such as selenium red, can be employed, therebyenabling manufacture of a photovoltaic film at low cost. In addition,since an organic substance is not employed in the photovoltaic filmmaterial, problems arising from employment of a sensitizing dyeconstituted of an organic substance (e.g., problems with regard to auseful life and light resistance of the sensitizing dye, and a problemof discoloration of a sensitizing dye caused by moisture) will beprevented. Furthermore, since the only requirements are to form thephotovoltaic film material manufactured in accordance with themanufacturing method of the invention into coating fluid and to coat thesame on a conductive film, the baking step can be omitted from formationof a photovoltaic film, thereby enabling reduction of manufacturing costalso in this regard. In addition, the amount of titanium dioxideparticles coated on the surface of the inorganic material particles canbe adjusted by means of adjusting the concentration of the titaniumhydroxide sol in the aqueous solution during the mixture preparationstep. The baking temperature in the baking step is preferably set to200° C. or higher.

Alternatively, the fourteenth aspect may be defined as providing “amethod for manufacturing a photovoltaic film material for use in aphotovoltaic film to be disposed in a solar cell, characterized byincluding: a production-material formation step of producing aprecipitated product material by means of producing an aqueous solutionhaving titanium hydroxide, powder consisting of inorganic materialparticles—which are particles of an inorganic material—, and lithiumchloride, and leaving the thus-produced aqueous solution; a drying stepof drying the product material formed in the product-material formationstep; and a baking step of baking the product material dried in thedrying step, thereby producing a photovoltaic film material.”

Alternatively, the fourteenth aspect may be defined as providing “amethod for manufacturing a photovoltaic film material for use in aphotovoltaic film to be disposed in a solar cell, characterized byincluding: a production-material formation step of producing aprecipitated product material by means of preparing titanium hydroxide,and powder consisting of inorganic material particles—which areparticles of an inorganic material—and an aqueous solution, and leavingto stand the thus-produced aqueous solution; and a baking step of bakingthe product material produced in the production-material formation step,thereby producing a photovoltaic film material.”

Alternatively, the fourteenth aspect may be defined as providing “amethod for manufacturing a photovoltaic film material for use in aphotovoltaic film to be disposed in a solar cell, characterized byincluding: a production-material formation step of producing aprecipitated product material by means of preparing titanium hydroxide,powder consisting of and inorganic material particles—which areparticles of an inorganic material—and an aqueous solution, and leavingto stand the thus-produced aqueous solution; a drying step of drying theproduct material produced in the product-material formation step; and abaking step of baking the product material dried in the drying step,thereby producing a photovoltaic film material.”

A fifteenth aspect is characterized in that, in the thirteenth orfourteenth aspect, the inorganic material which constitutes theinorganic material particles is an inorganic pigment, a metal, or ametal oxide. Meanwhile, the fifteenth aspect may alternatively bedefined as “being characterized in that, in the thirteenth or fourteenthaspect, the inorganic material particles are inorganic pigmentparticles, metal particles, or metal oxide particles.” Alternatively,the fifteenth aspect may be defined as “being characterized in that theinorganic material particles of the thirteenth or fourteenth aspect areparticles of a metal oxide, such as red iron oxide, yellow iron oxide,or black iron oxide, or metal particles.”

A sixteenth aspect is characterized in that, in the thirteenth,fourteenth, or fifteenth aspect, the method for manufacturing aphotovoltaic film material further includes acoating-fluid-like-material production step of producing acoating-fluid-like photovoltaic film material by means of mixing thephotovoltaic film material into an aqueous solution obtained by means ofmixing titanium hydroxide gel and aqueous hydrogen peroxide.

A seventeenth aspect is characterized in that, in the thirteenth,fourteenth, or fifteenth aspect, the method for manufacturing aphotovoltaic film material further includes acoating-fluid-like-material production step of producing acoating-fluid-like photovoltaic film material by means of mixing theproduced photovoltaic film material into a lithium silicate aqueoussolution.

An eighteenth aspect is characterized in that, in the thirteenth,fourteenth, or fifteenth aspect, the method for manufacturing aphotovoltaic film material further includes acoating-fluid-like-material production step of producing acoating-fluid-like photovoltaic film material by means of mixing thephotovoltaic film material into a mixture solution in which an aqueoussolution—obtained by means of mixing titanium hydroxide gel and aqueoushydrogen peroxide-and lithium silicate are mixed.

A nineteenth aspect provides a method for manufacturing a photovoltaicfilm to be disposed on a solar cell, characterized by including acoating step of coating a photovoltaic film material manufactured inaccordance with the method for manufacturing a photovoltaic filmmaterial defined in the fifteenth, sixteenth, seventeenth, or eighteenthaspect onto a conductive film serving as an electrode; and a baking stepof baking the photovoltaic film material having been coated in thecoating step. The baking temperature in the baking step is preferablyset to 200° C. or higher.

A twentieth aspect provides a method for manufacturing a photovoltaicfilm to be disposed on a solar cell, characterized by including acoating step of coating a photovoltaic film material manufactured inaccordance with the method for manufacturing a photovoltaic filmmaterial defined in the fifteenth, sixteenth, seventeenth, or eighteenthaspect onto a conductive film serving as an electrode.

Meanwhile, still another aspect may be defined as providing “a methodfor manufacturing a solar cell, characterized by including a coatingstep of coating a photovoltaic film material manufactured in accordancewith the method for manufacturing a photovoltaic film material definedin the fifteenth, sixteenth, seventeenth, or eighteenth aspect onto aconductive film serving as an electrode; and a baking step of baking thephotovoltaic film material coated in the coating step.” Alternatively,the same may be defined as providing “a method for manufacturing a solarcell, characterized by including a coating step of coating aphotovoltaic film material manufactured in accordance with the methodfor manufacturing a photovoltaic film material defined in the fifteenth,sixteenth, seventeenth, or eighteenth aspect onto a conductive filmserving as an electrode.”

Meanwhile, in the above respective aspects, the term“coating-fluid-like” may also be replaced with “paste-like.”

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view showing an essential portion of adye-sensitized solar cell.

BEST MODE FOR IMPLEMENTING THE INVENTION

Embodiments serving as working modes of the invention will be describedby reference to the drawing.

First, a first embodiment will be described. A photovoltaic film (may bereferred to as a “solar cell film”) of a solar cell (more specifically,a dye-sensitized solar cell) in the first embodiment is a red coatingwhose main ingredients are photocatalyst-coated particles which areselenium red particles (mean particle size: about 0.5 μm) on the surfaceof which titanium dioxide particles (mean particle size: about 6 nm) areabsorbed and disposed. Furthermore, the photocatalyst-coated particlesare formed such that lithium particles are attached to the surface ofthe selenium red particles and to the surface of the titanium dioxideparticles. A coating formed by means of applying thephotocatalyst-coated particles on a conductive glass plate with use oftitanium hydroxide (amorphous sol) as a binder is used as a photovoltaicfilm. The selenium red particles correspond to inorganic materialparticles; and the titanium dioxide particles correspond tophotocatalyst particles.

In other words, the photovoltaic film is formed by means of coating aphotovoltaic film material (may be referred to as a “coating material”),which will be described later, on a conductive glass plate and dryingthe same; or by means of coating the photovoltaic film material on aconductive glass plate, drying, and thereafter baking the same.Meanwhile, in the case where such baking operation is performed,titanium hydroxide serving as a binder is changed to titanium dioxidethrough baking; accordingly, in a stage of a photovoltaic film, thephotovoltaic film can be said to be formed from the photocatalyst-coatedparticles and titanium dioxide particles. In addition, in a case wherethe photovoltaic film material is merely coated onto the conductiveglass plate and dried without performing baking operation, thephotovoltaic film is configured so as to have the photocatalyst-coatedparticles and titanium hydroxide (amorphous sol).

Here, descriptions about the photovoltaic film material will beprovided. The photovoltaic film material is a product of suspension andkneading of the photocatalyst-coated particles in a mixture of ethanoland a light-yellow aqueous solution (hereinbelow, simply called a“light-yellow aqueous solution”) (specific gravity: about 1.3, solidcontent: 2%) synthesized by means of adding aqueous hydrogen peroxideinto titanium hydroxide (Ti(OH)₄) gel; and is formed into paste.

Meanwhile, the photocatalyst-coated particles are selenium red particles(mean particle size: about 0.5 μm) (inorganic material particles) on thesurface of which titanium dioxide particles (mean particle size: about 6nm) are absorbed and disposed. Lithium particles are attached onto thesurface of the selenium red particles and onto the surface of thetitanium dioxide particles. In other words, the titanium dioxideparticles—to the surface of which the lithium particles are attached—andthe lithium particles are attached to the surface of the selenium redparticles. Meanwhile, with regard to an extent of attachment of thelithium particles to the titanium dioxide particles, there are caseswhere lithium particles on individual titanium dioxide particles coatthe surface of a titanium dioxide particle, and there are other caseswhere lithium particles partially cover the surface of a titaniumdioxide particle. In short, the extent of attachment of the lithiumparticles onto the titanium dioxide particles varies among theindividual titanium dioxide particles in a photovoltaic film material.

In the above, the titanium dioxide particles are caused to be absorbedand disposed on the surface of the selenium red particles; however,particles of another metal oxide, such as red iron oxide particles,yellow iron oxide particles, or black iron oxide particles, or furtheralternatively metal particles, may be employed in place of the seleniumred particles. More specifically, an essential requirement for theparticles on which the titanium dioxide particles are absorbed anddisposed is to be inorganic material particles, such as inorganicpigment particles (may be referred to as inorganic dye particles); thatis, to be inorganic material particles—which are particles of aninorganic material. Meanwhile, in the invention, an inorganic materialencompasses inorganic pigments, metal oxides, and metals; and inorganicmaterial particles encompasses all inorganic pigment particles, metaloxide particles, and metal particles (this also applies to otherembodiments). In addition, in a photovoltaic film or a photovoltaic filmmaterial, particles of an inorganic material, such as selenium red, arein a state of being oxidized through a baking step, which will bedescribed later; that is, in a state of particles of an oxidizedinorganic material, such as a metal oxide.

A method for manufacturing the photovoltaic film in the first embodimentwill be described. First, 6 g of powder of selenium red (mean particlesize: about 0.5 μm, specific gravity: about 1.8) is uniformly dispersedin 600 mL (milliliter, the same applies hereinafter) of water by meansof ultrasonication, thereby preparing a predetermined amount of aselenium-red dispersion. Meanwhile, 50.2 g of a light-yellow aqueoussolution (specific gravity: about 1.3, solid content: 2%) synthesized bymeans of addition of aqueous hydrogen peroxide into titanium hydroxide(Ti (OH)₄) gel is uniformly dispersed in 600 mL of water. In this case,the titanium hydroxide gel is obtained by means of causing ammonia toreact with titanium tetrachloride. When aqueous hydrogen peroxide isadded to the titanium hydroxide gel, bubbling occurs; however, thisbubbling stops before long, thereby obtaining a viscous aqueoussolution. The solution is diluted, thereby obtaining the above-mentionedlight-yellow aqueous solution. Meanwhile, when aqueous hydrogen peroxideis added, titanium hydroxide gel is transformed into titanium hydroxidesol.

Next, the two solutions; that is, the selenium-red dispersion and thelight-yellow aqueous solutions, are mixed, thereby producing 1.2 L of amixture (a first mixture) (a first-mixture preparation step). Themixture can be said to be a mixture in which an aqueoussolution—obtained by means of mixing titanium hydroxide gel and aqueoushydrogen peroxide—, powder—consisting of inorganic material particleswhich are of an inorganic material—, and water are mixed (the same alsoapplies to any counterpart in the following embodiments). After themixture is stirred for one hour (stirring time is not limited to onehour, and may be set within a range of, e.g., thirty minutes to twohours) by an agitator (e.g., a stirrer), 10.7 g of 40% lithium chlorideaqueous solution is added, thereby preparing a second mixture (asecond-mixture preparation step). The second mixture can be said to bean aqueous solution having titanium hydroxide; powder of inorganicmaterial particles, which are particles of an inorganic material; andlithium chloride (the same also applies to any counterpart in thefollowing embodiments) The second mixture is slightly stirred, andcaused to be settled (alternatively, may be left to stand) for twohours, thereby causing precipitation of particles (a product-materialformation step (the precipitate corresponds to a product material).Meanwhile, the time of settlement is not limited to two hours, and maybe set within a range of, e.g., thirty minutes to three hours. The abovecondition can be readily ascertained from observation that a supernatanthaving been light-yellow-colored at the time of addition of thelight-yellow aqueous solution turns transparent after settlement. Whenthe surface of the selenium red is ascertained to be coated with thetitanium hydroxide, the supernatant portion is discarded by means ofdecantation; and the product material; that is, the precipitate, isheated at 100° C. for 10 hours (in the above description, thetemperature is set to 100° C.; however, no limitation is imposedthereon, and the temperature may be set within the range of 50° C. to150° C.; and the time of heating is set to 10 hours; however, nolimitation is imposed thereon (time of heating may be set within therange of 5 hours to 20 hours)), to thus be dried. Thereafter, theproduct material is baked in an inert atmosphere (e.g., in Ar gas flow(alternatively, in an Ar atmosphere), or in He gas flow (alternatively,in an He atmosphere), or in N₂ gas flow (alternatively, in an N₂atmosphere) at 500° C. for one hour (the baking step), thereby obtainingabout 6 g of red photocatalyst-coated particles. By virtue of havingsuch a configuration that titanium dioxide particles are absorbed andcoated on the surface of the selenium red particles, the redphotocatalyst-coated particles can react not only in the ultravioletlight wavelength range but also in the visible light wavelength range,thereby being wide-band-range-reaction-type photocatalyst particles.

Meanwhile, in preparation of the red photocatalyst-coated particles,baking operation is performed at 500° C.; however, an essentialrequirement for the baking temperature is to be 200° C. or higher. Thesame is more preferably set within the range of 200 to 700° C. Inaddition, in the above, the baking time is set to one hour; however, thebaking time may be set within a range of thirty minutes to three hours.

Worthy of special note is that, 4.28 g of lithium chloride in the formof solid content is added at the time of causing precipitation of theparticles; however, when the same is not added, the supernatant remainslight-yellow, and coating will be insufficient. The volume of theprecipitate in the case of lithium chloride being added is ten times ormore that in a case where the same not being added. This seems to beascribable to electrical properties of lithium ions and capabilities ofchloride ions. In addition, when, for the purpose of comparison,precipitation is caused for comparison by means of adding sodiumchloride or potassium chloride, on some occasions white salt crystalsappear during baking; however, such appearance does not occur in thecase of lithium chloride. Meanwhile, since baking operation is performedas described above, chlorine ions in lithium chloride evaporate. Incontrast, lithium ions in lithium chloride remain inphotocatalyst-coated particles in the form of lithium particles.Meanwhile, in the above description, a lithium chloride aqueous solutionis added; however, alternatively, lithium chloride itself may be addedin place of the aqueous solution (the same also applies to anycounterpart in the following embodiments).

Next, 5 g of the photocatalyst-coated particles obtained in the aboveproduction method is suspended and kneaded in a mixture consisting of 45mL of light-yellow aqueous solution (specific gravity: about 1.3, solidcontent: 2%) synthesized by means of adding aqueous hydrogen peroxide totitanium hydroxide (Ti (OH)₄) gel, and 5 mL of ethanol, therebypreparing paste for producing a photovoltaic film (a coating-fluid-likematerial preparation step). Meanwhile, when aqueous hydrogen peroxide isadded, titanium hydroxide gel is transformed into titanium hydroxidesol. The paste serves as the photo voltaic film material. The paste iscoated on a conductive glass plate (ITO) (that is, the conductive filmon a conductive glass plate on which a conductive film serving as anelectrode is disposed) with use of a spray gun, and dried, therebypreparing a photovoltaic film. The coating operation of the paste ontothe conductive glass corresponds to a coating step.

Meanwhile, the paste may be merely coated on a conductive glass plateand dried; alternatively, the paste may be baked after being coated on aconductive glass plate and dried. This baking operation corresponds tothe baking step. Conditions for performing such baking are 480 Celsius,in an inert atmosphere, and for one hour. In the case where such bakingoperation is performed, titanium hydroxide serving as a binder arechanged to titanium dioxide through baking; accordingly, in a stage ofbeing formed into a photovoltaic film, the photovoltaic film can be saidto be formed from the photocatalyst-coated particles and titaniumdioxide particles. Meanwhile, in the above description, the bakingoperation is performed at 480° C. for one hour; however, no limitationis imposed thereon, and an essential requirement for the bakingtemperature is to be, e.g., 200° C. or higher, and more preferably thebaking temperature falls within the range of 200° C. to 700° C. Inaddition, an essential requirement for the baking time is to fall, e.g.,within the range of thirty minutes to three hours.

Incidentally, in the above manufacturing method, the amount of titaniumdioxide particles coated on the surface of selenium red particles can beadjusted by means of adjusting the concentration of the titaniumhydroxide sol in the light-yellow aqueous solution. For instance, theamount of the titanium dioxide particles can be increased by means ofincreasing the concentration of the titanium hydroxide sol. Morespecifically, by means of adjusting the amount of titanium hydroxide gelto react with aqueous hydrogen peroxide, and/or the volume of waterserving as a solvent for performing dilution, the concentration of thetitanium hydroxide sol can be adjusted, thereby enabling adjustment ofthe amount of the titanium dioxide particles coated on the surface ofthe selenium red particles, which serve as inorganic material particles.In addition, the amount of titanium dioxide particles coated on thesurface of selenium red particles can also be adjusted by means ofadjusting the concentration of the selenium red in a dispersion solutionin which powder of the inorganic material particles (more specifically,powder of selenium red) is dispersed. For instance, the amount oftitanium dioxide particles coated on the surface of a single seleniumred particle can be reduced by means of increasing the concentration ofa pigment.

In addition, also in the case where the light-yellow aqueous solutionsynthesized by means of adding aqueous hydrogen peroxide into titaniumhydroxide (Ti (OH)₄) gel is used as a binder, coating strength of thephotovoltaic film can be adjusted by means of adjusting theconcentration of titanium hydroxide sol in the light-yellow aqueoussolution.

In addition, the amount of titanium dioxide in the photovoltaic film canbe adjusted also by means of adjusting the amount of thephotocatalyst-coated particles in relation to the mixture when thephotocatalyst-coated particles are suspended and kneaded into themixture constituted of the light-yellow aqueous solution (specificgravity: about 1.3, solid content: 2%) having been synthesized by meansof adding aqueous hydrogen peroxide to titanium hydroxide (Ti(OH)₄) gel,and ethanol.

Meanwhile, in the above manufacturing method, selenium red is adopted asan inorganic material; however, there may be adopted another metal oxideor another inorganic pigment, or a metal (that is, a metal material maybe adopted).

Meanwhile, a solar cell employing the photovoltaic film of the presentembodiment has the same basic configuration as that in the related art,and is configured, e.g., as shown in FIG. 1. More specifically, on asolar cell A of the present embodiment, a photovoltaic film (mayalternatively be referred to as a coating) 30 of the above configurationis disposed. In relation to working effects of the photovoltaic film ofthe present embodiment, selenium red particles in thephotocatalyst-coated particles function as a sensitizing dye. When lightimpinges on the selenium red particles (it should be noted that seleniumred particles are covered with titanium dioxide particles, and that thephotocatalyst-coated particles are present among the binder, or, in acase where baking operation is performed, present in the titaniumdioxide; however, in actuality, since gaps are present among particlesof the titanium dioxide (in a case where baking operation is notperformed, in titanium hydroxide) particles, light reaches the seleniumred particles), the selenium red is excited in terms of energy, and thethus-generated excitation energy is transmitted in the form of electronsto the titanium dioxide particles which coat the selenium red. Theelectrons are sequentially transmitted from one titanium dioxideparticle to another, thereby reaching a conductive glass plate 10, tothus be transferred to a conductive glass plate 20 on the counterelectrode. The mechanism allows delivery of electric power at this time.The electrons having been transferred to the counter electrodesubsequently return to the sensitizing dye or to the titanium dioxideparticles by way of a redox reaction in the electrolytic solution. Itcan be said that an electromotive force is obtained through repetitionof this cycle.

Next, functionality of a solar cell employing the photovoltaic film ofthe first embodiment will be described briefly. Generation of anelectromotive force is ascertained under irradiation with artificialsunlight by use of a platinum conductive glass as a counter electrode ofan electrode on which the photovoltaic film is coated, and with use of0.5 M LiI, 0.05 M I₂,0.4 M 4-tertialy-butylpyridine,0.5MDMPII,3-metoxyacetonitril (solvent) as an electrolyte. As a result, a constantelectromotive force is obtained irrespective of whether or not thephotovoltaic film is subjected to baking operation; and a correlationdiagram between electric current and voltage indicates characteristicsof a battery.

In addition, the solar cell of the present embodiment generates anelectromotive force for a certain duration even after being placed in alight-shielded condition. This seems to be ascribable to capabilities oflithium particles in the photovoltaic film.

As described above, since the photovoltaic film and the photovoltaicfilm material of the solar cell in the present embodiment aremanufactured in accordance with the above-described manufacturingprocess, and can employ an inexpensive material, such as selenium red, aphotovoltaic film can be manufactured at low cost. In addition, since anorganic substance is not employed in the photovoltaic film and thephotovoltaic film material, problems arising from employment of asensitizing dye constituted of an organic substance (e.g., problems withregard to a useful life and light resistance of the sensitizing dye, anda problem of discoloration of a sensitizing dye caused by moisture) willbe prevented. Furthermore, in the case where the photovoltaic filmmaterial of the present embodiment is employed, a consistent result canbe obtained from formation of a photovoltaic film, irrespective ofwhether or not baking operation is performed; accordingly, a baking stepcan be omitted from formation of a photovoltaic film, thereby enablingreduction of manufacturing cost also in this regard.

In addition, in the present embodiment, since the aqueous solution oflithium chloride is employed in manufacture of the photovoltaic filmmaterial, absorption of titanium hydroxide into selenium red can beenhanced, thereby enabling sufficient coating of the titanium hydroxideonto the selenium red. In addition, since the photovoltaic film materialincludes the lithium particles, the presence of the lithium particlesenables maintenance of an electromotive force even under alight-shielded condition.

Next, a second embodiment will be described. A photovoltaic film (may bereferred to as a “solar cell film”) of a solar cell (more specifically,a dye-sensitized solar cell) of the second embodiment is a red coatingwhose main ingredients are photocatalyst-coated particles which areselenium red particles (mean particle size: about 0.5 μm) on the surfaceof which titanium dioxide particles (mean particle size: about 6 nm) areabsorbed and disposed. Furthermore, the photocatalyst-coated particlesare formed such that lithium particles are attached to the surface ofthe selenium red particles and to the surface of the titanium dioxideparticles. A coating formed by means of applying thephotocatalyst-coated particles on a conductive glass plate with use oflithium silicate as a binder is used as a photovoltaic film. Morespecifically, the photovoltaic film of the present embodiment includesthe above-mentioned photocatalyst-coated particles and lithium silicateparticles. The selenium red particles correspond to inorganic materialparticles; and the titanium dioxide particles correspond tophotocatalyst particles.

The photovoltaic film is formed by means of coating a photovoltaic filmmaterial, which will be described later, on a conductive glass plate anddrying the same; or by means of coating the photovoltaic film materialon a conductive glass plate, drying, and thereafter baking the same.

Here, descriptions of the photovoltaic film material will be provided.The photovoltaic film material is a product of suspension and kneadingof the photocatalyst-coated particles in a mixture of a lithium silicateand purified water; and is formed into paste.

Meanwhile, the photocatalyst-coated particles are selenium red particles(mean particle size: about 0.5 μm) (inorganic material particles) on thesurface of which titanium dioxide particles (mean particle size: about 6nm) are absorbed and disposed. Lithium particles are attached onto thesurface of the selenium red particles and onto the surface of thetitanium dioxide particles. In other words, the titanium dioxideparticles—on the surface of which the lithium particles are attached—andthe lithium particles are attached on the surface of the selenium redparticles. Meanwhile, with regard to an extent of attachment of thelithium particles onto the titanium dioxide particles, there are caseswhere lithium particles on individual titanium dioxide particles coatthe surfaces of a titanium dioxide particle, and there are other caseswhere lithium particles partially cover the surface of a titaniumdioxide particle. That is, the extent of attachment of the lithiumparticles onto the titanium dioxide particles varies among theindividual titanium dioxide particles in a photovoltaic film material.

In the above description, the titanium dioxide particles are caused tobe absorbed and disposed on the surface of the selenium red particles;however, particles of another metal oxide, such as red iron oxideparticles, yellow iron oxide particles, or black iron oxide particles,or further alternatively metal particles, may be employed in place ofthe selenium red particles. More specifically, an essential requirementfor the particles on which the titanium dioxide particles are absorbedand disposed is to be inorganic material particles, such as inorganicpigment particles (may be referred to as inorganic dye particles); thatis, to be inorganic material particles—which are particles of aninorganic material. Meanwhile, in a photovoltaic film or a photovoltaicfilm material, particles of an inorganic material, such as selenium red,are in a state of being oxidized through a baking step, which will bedescribed later; that is, in a state of particles of an oxidizedinorganic material, such as a metal oxide.

A method for manufacturing the photovoltaic film of the secondembodiment will be described. First, photocatalyst-coated particles areprepared. The method for preparing the photocatalyst-coated particles isthe same as that in the first embodiment. More specifically, first, 6 gof powder of selenium red (mean particle size: about 0.5 μm, specificgravity: about 1.8) is uniformly dispersed in 600 mL (milliliter, thesame applies hereinafter) of water by means of ultrasonication, therebypreparing a predetermined amount of a selenium-red dispersion.Meanwhile, 50.2 g of a light-yellow aqueous solution (specific gravity:about 1.3, solid content: 2%) synthesized by means of addition ofaqueous hydrogen peroxide into titanium hydroxide (Ti (OH)₄) gel isuniformly dispersed in 600 mL of water. In this case, the titaniumhydroxide gel is obtained by means of causing ammonia to react withtitanium tetrachloride. When aqueous hydrogen peroxide is added to thetitanium hydroxide gel, bubbling occurs; however, this bubbling stopsbefore long, thereby obtaining a viscous aqueous solution. The solutionis diluted, thereby obtaining the above-mentioned light-yellow aqueoussolution. Meanwhile, when aqueous hydrogen peroxide is added, titaniumhydroxide gel is transformed into titanium hydroxide sol.

Next, the two solutions; that is, the selenium-red-dispersed solutionand the light-yellow aqueous solution, are mixed, thereby producing 1.2L of a mixture (a first mixture) (a first-mixture preparation step).After the mixture is stirred for one hour (stirring time is not limitedto one hour, and may be set within a range of, e.g., thirty minutes totwo hours) by an agitator (e.g., a stirrer), 10.7 g of 40% lithiumchloride aqueous solution is added, thereby preparing a second mixture(a second-mixture preparation step). The second mixture is slightlystirred, and caused to be settled (alternatively, may be left to stand)for two hours, thereby causing precipitation of particles (aproduct-material formation step (the precipitate corresponds to aproduct material). The time of settlement is not limited to two hours,and may be set within a range of, e.g., thirty minutes to three hours).The above condition can be readily ascertained from observation that asupernatant having been light-yellow-colored at the time of addition ofthe light-yellow aqueous solution turns transparent after settlement.When the surface of the selenium red is ascertained to be coated withthe titanium hydroxide, the supernatant portion is discarded by means ofdecantation; and the product material; that is, the precipitate, isheated at 100° C. for 10 hours (in the above description, thetemperature is set to 100° C.; however, no limitation is imposedthereon, and the temperature may be set within the range of 50° C. to150° C.; and the time of heating is set to 10 hours; however, nolimitation is imposed thereon (the time of heating may be set within therange of 5 hours to 20 hours)), to thus be dried. Thereafter, theproduct material is baked in an inert atmosphere (in Ar gas flow(alternatively, in an Ar atmosphere), or in He gas flow (alternatively,in an He atmosphere), or in N₂ gas flow (alternatively, in an N₂atmosphere)) at 500° C. for one hour (the baking step), therebyobtaining about 6 g of red photocatalyst-coated particles. By virtue ofhaving such a configuration that titanium dioxide particles are absorbedand coated on the surface of the selenium red particles, the redphotocatalyst-coated particles can react not only in the ultravioletlight wavelength range, but also in the visible light wavelength range,thereby being wide-band-range-reaction-type photocatalyst particles.

Meanwhile, in preparation of the red photocatalyst-coated particles,baking operation is performed at 500° C.; however, an essentialrequirement for the baking temperature is to be 200° C. or higher. Thesame is more preferably set within the range of 200° C. to 700° C. Inaddition, in the above, the baking time is set to one hour; however, thebaking time may be set within a range of thirty minutes to three hours.

Worthy of special note is that, 4.28 g of lithium chloride in the formof solid content is added at the time of causing precipitation of theparticles; however, when the same is not added, the supernatant remainslight-yellow, and coating will be insufficient. The volume of theprecipitate in the case of lithium chloride being added is ten times ormore that in a case where the same is not added. This seems to beascribable to electrical properties of lithium ions and capabilities ofchloride ions. In addition, when, for the purpose of comparison,precipitation is caused by means of adding sodium chloride or potassiumchloride, on some occasions white salt crystals appear during baking;however, such appearance does not occur in the case of lithium chloride.Meanwhile, since baking operation is performed as described above,chlorine ions in lithium chloride evaporate. In contrast, lithium ionsin lithium chloride remain in photocatalyst-coated particles in the formof lithium particles. Meanwhile, in the above description, a lithiumchloride aqueous solution is added; however, alternatively, lithiumchloride itself may be added in place of the aqueous solution.

Next, 5 g of photocatalyst-coated particles obtained in the above methodis suspended and kneaded in a mixture consisting of 2.7 g of lithiumsilicate (SiO₂ content: 20 to 21%) and 48.3 g of purified water, therebypreparing a paste for producing a photovoltaic film. More specifically,a paste for producing a photovoltaic film is prepared by means ofsuspending and kneading the photocatalyst-coated particles into amixture consisting of lithium silicate and purified water (acoating-fluid-like material preparation step). The paste is coated on aconductive glass plate (ITO) (that is, the conductive film on aconductive glass plate on which a conductive film serving as anelectrode is disposed) with use of a spray gun, and dried, therebypreparing a photovoltaic film. The coating operation of the paste ontothe conductive glass corresponds to a coating step.

Meanwhile, the paste may be merely coated on a conductive glass plateand dried; alternatively, the paste may be baked after being coated on aconductive glass plate and dried. This baking operation corresponds tothe baking step. Conditions for performing baking are 480 Celsius, in aninert atmosphere, and for one hour. Meanwhile, in the above description,the baking operation is performed at 480° C. for one hour; however, nolimitation is imposed thereon, and an essential requirement for thebaking temperature is to be, e.g., 200° C. or higher, and morepreferably, the baking temperature falls within the range of 200° C. to700° C. In addition, an essential requirement for the baking time is tofall, e.g., within the range of thirty minutes to three hours.

Also in the second embodiment, as in the case of the first embodiment,in the above manufacturing method, the amount of titanium dioxideparticles coated on the surface of selenium red particles can beadjusted by means of adjusting the concentration of the titaniumhydroxide sol in the light-yellow aqueous solution. In addition, theamount of titanium dioxide particles coated on the surface of seleniumred particles can also be adjusted by means of adjusting theconcentration of the selenium red in a dispersion solution in whichpowder of the inorganic material particles (more specifically, powder ofselenium red) is dispersed.

In addition, the amount of titanium dioxide in the photovoltaic film canalso be adjusted by means of adjusting the amount of thephotocatalyst-coated particles in relation to the mixture when thephotocatalyst-coated particles are suspended and kneaded in the mixtureconstituted of lithium silicate and purified water.

Meanwhile, in the above manufacturing method, selenium red is adopted asan inorganic material; however, there may be adopted another metal oxideor another inorganic pigment, or a metal (that is, a metal material maybe adopted).

Meanwhile, a solar cell employing the photovoltaic film of the presentembodiment has the same basic configuration as that in the related art,and is configured, e.g., as shown in FIG. 1. More specifically, on asolar cell A of the present embodiment, a photovoltaic film (mayalternatively be referred to as a coating) 30 of the above configurationis disposed. The working effects of the photovoltaic film of the presentembodiment are the same as those of the first embodiment. Morespecifically, selenium red particles in the photocatalyst-coatedparticles function as a sensitizing dye. When light impinges on theselenium red particles (it should be noted that the selenium redparticles are covered with titanium dioxide particles, and that thephotocatalyst-coated particles are present in the binder; however, inactuality, since gaps are present among particles of the titaniumdioxide and those of the lithium silicate, light reaches the seleniumred particles), the selenium red is excited in terms of energy, and thethus-generated excitation energy is transmitted in the form of electronsto the titanium dioxide particles which coat the selenium red particles.The electrons are sequentially transmitted from one titanium dioxideparticle to another, thereby reaching a conductive glass plate 10, tothus be transferred to a conductive glass plate 20 on the counterelectrode. The mechanism allows delivery of electric power at this time.The electrons having been transferred to the counter electrodesubsequently return to the sensitizing dye or to the titanium dioxideparticles by way of a redox reaction in the electrolytic solution. Itcan be said that an electromotive force is obtained through repetitionof this cycle.

Next, functionality of a solar cell employing the photovoltaic film ofthe second embodiment will be briefly described. Generation of anelectromotive force is ascertained under irradiation of artificialsunlight with use of a platinum conductive glass as a counter electrodeof an electrode on which the photovoltaic film is coated, and with useof 0.5 M LiI,0.05 M I₂,0.4 M 4-tertialy-butylpyridine,0.5MDMPII,3-metoxyacetonitril (solvent) asanelectrolyte. As a result, a constantelectromotive force is obtained irrespective of whether or not thephotovoltaic film is subjected to baking operation; and a correlationdiagram between electric current and voltage indicates characteristicsof a battery.

In addition, the solar cell of the present embodiment generates anelectromotive force for a certain duration even after being placed in alight-shielded condition. This seems to be ascribable to capabilities oflithium particles in the photovoltaic film.

As described above, since the photovoltaic film and the photovoltaicfilm material of the solar cell in the present embodiment aremanufactured in accordance with the above-described manufacturingprocess, and can employ an inexpensive material, such as selenium red, aphotovoltaic film can be manufactured at low cost. In addition, since anorganic substance is not employed in the photovoltaic film and thephotovoltaic film material, problems arising from employment of asensitizing dye constituted of an organic substance (e.g., problems withregard to a useful life and light resistance of the sensitizing dye, anda problem of discoloration of a sensitizing dye caused by moisture) willbe prevented. Furthermore, in the case where the photovoltaic filmmaterial of the present embodiment is employed, a consistent result canbe obtained from formation of a photovoltaic film, irrespective ofwhether or not baking operation is performed; accordingly, a baking stepcan be omitted from formation of a photovoltaic film, thereby enablingreduction of manufacturing cost also in this regard.

In addition, in the present embodiment, since the aqueous solution oflithium chloride is employed in manufacture of the photovoltaic filmmaterial, absorption of titanium hydroxide into selenium red can beenhanced, thereby enabling sufficient coating of the titanium hydroxideonto the selenium red. In addition, since the photovoltaic film materialincludes the lithium particles, the presence of the lithium particlesenables maintenance of an electromotive force even under alight-shielded condition.

Next, a third embodiment will be described. A photovoltaic film (may bereferred to as a “solar cell film”) of a solar cell (more specifically,a dye-sensitized solar cell) of the third embodiment is a red coatingwhose main ingredients are photocatalyst-coated particles which areselenium red particles (mean particle size: about 0.5 μm) on the surfaceof which titanium dioxide particles (mean particle size: about 6 nm) areabsorbed and disposed. Furthermore, the photocatalyst-coated particlesare formed such that lithium particles are attached to the surface ofthe selenium red particles and to the surface of the titanium dioxideparticles. A coating formed by means of applying thephotocatalyst-coated particles on a conductive glass plate with use oftitanium hydroxide (amorphous sol) and lithium silicate as a binder isused as a photovoltaic film. Meanwhile, the selenium red particlescorrespond to inorganic material particles; and the titanium dioxideparticles correspond to photocatalyst particles.

More specifically, the photovoltaic film is formed by means of coating aphotovoltaic film material, which will be described later, on aconductive glass plate and drying the same; or by means of coating thephotovoltaic film material on a conductive glass plate, drying, andthereafter baking the same. Meanwhile, in the case where such bakingoperation is performed, titanium hydroxide serving as a binder istransformed to titanium dioxide through baking; accordingly, in a stageof formation of a photovoltaic film, the photovoltaic film can be saidto be formed from the photocatalyst-coated particles, titanium dioxideparticles, and lithium silicate. In addition, in a case where thephotovoltaic film material is merely coated onto the conductive glassplate and dried without performing baking operation, the photovoltaicfilm is configured so as to have the photocatalyst-coated particles,titanium hydroxide (amorphous sol), and lithium silicate.

Here, descriptions about the photovoltaic film material will beprovided. The photovoltaic film material is a product of suspension andkneading of the photocatalyst-coated particles in a mixture of lithiumsilicate and a light-yellow aqueous solution (hereinbelow, simply calleda “light-yellow aqueous solution”) (specific gravity: about 1.3, solidcontent: 2%) synthesized by means of adding aqueous hydrogen peroxideinto titanium hydroxide (Ti(OH)₄) gel; and is formed into paste.

Meanwhile, the photocatalyst-coated particles are selenium red particles(mean particle size: about 0.5 μm) (inorganic material particles) on thesurface of which titanium dioxide particles (mean particle size: about 6nm) are absorbed and disposed. Lithium particles are attached onto thesurface of the selenium red particles and onto the surface of thetitanium dioxide particles. In other words, the titanium dioxideparticles—on the surface of which the lithium particles are attached—andthe lithium particles are attached on the surface of the selenium redparticles. Meanwhile, with regard to an extent of attachment of thelithium particles onto the titanium dioxide particles, there are caseswhere lithium particles on individual titanium dioxide particles coatthe surfaces of a titanium dioxide particle, and there are other caseswhere lithium particles partially cover the surface of titanium dioxide.That is, the extent of attachment of the lithium particles onto thetitanium dioxide particles varies among the individual titanium dioxideparticles in a photovoltaic film material.

In the above, the titanium dioxide particles are caused to be absorbedand disposed on the surface of the selenium red particles; however,particles of another metal oxide, such as red iron oxide particles,yellow iron oxide particles, or black iron oxide particles, or furtheralternatively metal particles, may be employed in place of the seleniumred particles. More specifically, an essential requirement for theparticles on which the titanium dioxide particles are absorbed anddisposed is to be inorganic material particles, such as inorganicpigment particles (may be referred to as inorganic dye particles); thatis, to be inorganic material particles—which are particles of aninorganic material. Meanwhile, in a photovoltaic film or a photovoltaicfilm material, particles of an inorganic material, such as selenium red,are in a state of being oxidized through a baking step, which will bedescribed later; that is, in a state of particles of an oxidizedinorganic material, such as a metal oxide.

A method for manufacturing the photovoltaic film of the third embodimentwill be described. First, 6 g of powder of selenium red (mean particlesize: about 0.5 μm, specific gravity: about 1.8) is uniformly dispersedin 600 mL (milliliter, the same applies hereinafter) of water by meansof ultrasonication, thereby preparing a predetermined amount of aselenium-red dispersion. Meanwhile, 50.2 g of a light-yellow aqueoussolution (specific gravity: about 1.3, solid content: 2%) synthesized bymeans of addition of aqueous hydrogen peroxide into titanium hydroxide(Ti (OH)₄) gel is uniformly dispersed in 600 mL of water. In this case,the titanium hydroxide gel is obtained by means of causing ammonia toreact with titanium tetrachloride. When aqueous hydrogen peroxide isadded to the titanium hydroxide gel, bubbling occurs; however, thisbubbling stops before long, thereby obtaining a viscous aqueoussolution. The solution is diluted, thereby obtaining the above-mentionedlight-yellow aqueous solution. Meanwhile, when aqueous hydrogen peroxideis added, titanium hydroxide gel is transformed into titanium hydroxidesol.

Next, the two solutions; that is, the selenium-red-dispersed solutionand the light-yellow aqueous solution, are mixed, thereby producing 1.2L of a mixture (a first mixture) (a first-mixture preparation step).After the mixture is stirred for one hour (stirring time is not limitedto one hour, and may be set within a range of, e.g., thirty minutes totwo hours) by an agitator (e.g., a stirrer), 10.7 g of 40% lithiumchloride aqueous solution is added, thereby preparing a second mixture(a second-mixture preparation step). The second mixture is slightlystirred, and caused to be settled (alternatively, may be left to stand)for two hours, thereby causing precipitation of particles (aproduct-material formation step (the precipitate corresponds to aproduct material). The time of settlement is not limited to two hours,and may be set within a range of, e.g., thirty minutes to three hours).The above condition can be readily ascertained from observation that asupernatant having been light-yellow-colored at the time of addition ofthe light-yellow aqueous solution turns transparent after settlement.When the surface of the selenium red is ascertained to be coated withthe titanium hydroxide, the supernatant portion is discarded by means ofdecantation; and the product material; that is, the precipitate, isheated at 100° C. for 10 hours (in the above description, thetemperature is set to 100° C.; however, no limitation is imposedthereon, and the temperature may be set within the range of 50° C. to150° C.; and the time of heating is set to 10 hours; however, nolimitation is imposed thereon (the time of heating may be set within therange of 5 hours to 20 hours)), to thus be dried. Thereafter, theproduct material is baked in an inert atmosphere (in Ar gas flow(alternatively, in an Ar atmosphere), or in He gas flow (alternatively,in an He atmosphere), or in N₂ gas flow (alternatively, in an N₂atmosphere) at 500° C. for one hour (the baking step), thereby obtainingabout 6 g of red photocatalyst-coated particles. By virtue of havingsuch a configuration that titanium dioxide particles are absorbed andcoated on the surface of the selenium red particles, the redphotocatalyst-coated particles can react not only in the ultravioletlight wavelength range, but also in the visible light wavelength range,thereby being wide-band-range-reaction-type photocatalyst particles.

Meanwhile, in preparation of the red photocatalyst-coated particles,baking operation is performed at 500° C.; however, an essentialrequirement for the baking temperature is to be 200° C. or higher. Thesame is more preferably set within the range of 200° C. to 700° C. Inaddition, in the above, the baking time is set to one hour; however, thebaking time may be set within a range of thirty minutes to three hours.

Worthy of special note is that, 4.28 g of lithium chloride in the formof solid content is added at the time of causing precipitation of theparticles; however, when the same is not added, the supernatant remainslight-yellow, and coating will be insufficient. The volume of theprecipitate in the case of lithium chloride being added is ten times ormore that in a case where the same is not added. This seems to beascribable to electrical properties of lithium ions and capabilities ofchloride ions. In addition, when, for the purpose of comparison,precipitation is caused by means of adding sodium chloride or potassiumchloride, on some occasions white salt crystals appear during baking;however, such appearance does not occur in the case of lithium chloride.Meanwhile, since baking operation is performed as described above,chlorine ions in lithium chloride evaporate. In contrast, lithium ionsin lithium chloride remain in photocatalyst-coated particles in the formof lithium particles. Meanwhile, in the above description, a lithiumchloride aqueous solution is added; however, alternatively, lithiumchloride itself may be added in place of the aqueous solution.

Next, 5 g of photocatalyst-coated particles obtained in the above methodis suspended and kneaded in a mixture consisting of 2.7 g of lithiumsilicate (SiO₂ content: 20 to 21%) and 50 g of a light-yellow aqueoussolution (specific gravity: about 1.3, solid content: 2%) synthesized bymeans of adding aqueous hydrogen peroxide to titanium hydroxide (Ti(OH)₄) gel, thereby preparing paste for producing a photovoltaic film (acoating-fluid-like material preparation step). More specifically, thephotocatalyst particles are suspended and kneaded in a mixtureconsisting of lithium silicate and the light-yellow aqueous solution.Meanwhile, when aqueous hydrogen peroxide is added, titanium hydroxidegel is transformed into titanium hydroxide sol. The paste serves as thephotovoltaic film material. The paste is coated on a conductive glassplate (ITO) (that is, the conductive film on a conductive glass plate onwhich a conductive film serving as an electrode is disposed) with use ofa spray gun, and dried, thereby preparing a photovoltaic film. Thecoating operation of the paste onto the conductive glass corresponds toa coating step.

Meanwhile, the paste may be merely coated on a conductive glass plateand dried; alternatively, the paste may be baked after being coated on aconductive glass plate and dried. This baking operation corresponds tothe baking step. Conditions for performing such baking are 480 Celsius,in an inert atmosphere, and for one hour. In the case where such bakingoperation is performed, titanium hydroxide serving as a binder istransformed to titanium dioxide through baking; accordingly, in a stageof being formed into a photovoltaic film, the photovoltaic film can besaid to be formed from the photocatalyst-coated particles and titaniumdioxide particles. Meanwhile, in the above description, the bakingoperation is performed at 480° C. for one hour; however, no limitationis imposed thereon, and an essential requirement for the bakingtemperature is to be, e.g., 200° C. or higher, and more preferably, thebaking temperature falls within the range of 200° C. to 700° C. Inaddition, an essential requirement for the baking time is to fall, e.g.,within the range of thirty minutes to three hours.

Also in the third embodiment, as in the case of the first embodiment orsecond embodiment, in the above manufacturing method, the amount oftitanium dioxide particles coated on the surface of selenium redparticles can be adjusted by means of adjusting the concentration of thetitanium hydroxide sol in the light-yellow aqueous solution. Inaddition, the amount of titanium dioxide particles coated on the surfaceof selenium red particles can also be adjusted by means of adjusting theconcentration of the selenium red in a dispersion solution in whichpowder of the inorganic material particles (more specifically, powder ofselenium red) is dispersed.

In addition, also in the case where the light-yellow aqueous solutionsynthesized by means of adding aqueous hydrogen peroxide into titaniumhydroxide (Ti(OH)₄) gel is used as a binder, coating strength of thephotovoltaic film can be adjusted by means of adjusting theconcentration of titanium hydroxide sol in the light-yellow aqueoussolution.

In addition, the amount of titanium dioxide particles in thephotovoltaic film can also be adjusted by means of adjusting the amountof the photocatalyst-coated particles in relation to the mixture whenthe photocatalyst-coated particles are suspended and kneaded in themixture constituted of the light-yellow aqueous solution (specificgravity: about 1.3, solid content: 2%) having been synthesized by meansof adding aqueous hydrogen peroxide to titanium hydroxide (Ti(OH)₄) gel,and lithium silicate.

Meanwhile, in the above manufacturing method, selenium red is adopted asan inorganic material; however, there may be adopted another metal oxideor another inorganic pigment, or a metal (that is, a metal material maybe adopted).

Meanwhile, a solar cell employing the photovoltaic film of the presentembodiment has the same basic configuration as that in the related art,and is configured, e.g., as shown in FIG. 1. More specifically, on asolar cell A of the present embodiment, a photovoltaic film (mayalternatively be referred to as a coating) 30 of the above configurationis disposed. The working effects of the photovoltaic film of the presentembodiment are the same as those of the first embodiment and those ofthe second embodiment. More specifically, selenium red particles in thephotocatalyst-coated particles function as a sensitizing dye. When lightimpinges on the selenium red particles, the selenium red is excited interms of energy, and the thus-generated excitation energy is transmittedin the form of electrons to the titanium dioxide particles which coatthe selenium red. The electrons are sequentially transmitted from onetitanium dioxide particle to another, thereby reaching a conductiveglass plate 10, to thus be transferred to a conductive glass plate 20 onthe counter electrode. The mechanism allows delivery of electric powerat this time. The electrons having been transferred to the counterelectrode subsequently return to the sensitizing dye or to the titaniumdioxide particles by way of a redox reaction in the electrolyticsolution. It can be said that an electromotive force is obtained throughrepetition of this cycle.

Next, functionality of a solar cell employing the photovoltaic film ofthe third embodiment will be briefly explained. Functionality of thesolar cell employing the photovoltaic film of the third embodiment willbe described with use of a platinum conductive glass as a counterelectrode of an electrode on which the photovoltaic film is coated, andwith use of 0.5 M LiI,0.05 M I₂,0.4M4-tertialy-butylpyridine,0.5MDMPII,3-metoxy acetonitril(solvent) as anelectrolyte. Generation of an electromotive force is ascertained underirradiation of artificial sunlight with use of the platinum conductiveglass as a counter electrode of the electrode on which the photovoltaicfilm is coated. As a result, a constant electromotive force is obtainedirrespective of whether or not the photovoltaic film is subjected tobaking operation; and a correlation diagram between electric current andvoltage indicates characteristics of a battery.

In addition, the solar cell of the present embodiment generates anelectromotive force for a certain duration even after being placed in alight-shielded condition. This seems to be ascribable to capabilities oflithium particles in the photovoltaic film.

As described above, since the photovoltaic film and the photovoltaicfilm material of the solar cell in the present embodiment aremanufactured in accordance with the above-described manufacturingprocess, and can employ an inexpensive material, such as selenium red, aphotovoltaic film can be manufactured at low cost. In addition, since anorganic substance is not employed in the photovoltaic film and thephotovoltaic film material, problems arising from employment of asensitizing dye constituted of an organic substance (e.g., problems withregard to a useful life and light resistance of the sensitizing dye, anda problem of discoloration of a sensitizing dye caused by moisture) willbe prevented. Furthermore, in the case where the photovoltaic filmmaterial of the present embodiment is employed, a consistent result canbe obtained from formation of a photovoltaic film, irrespective ofwhether or not baking operation is performed; accordingly, a baking stepcan be omitted from formation of a photovoltaic film, thereby enablingreduction of manufacturing cost also in this regard.

In addition, in the present embodiment, since the aqueous solution oflithium chloride is employed in manufacture of the photovoltaic filmmaterial, absorption of titanium hydroxide into selenium red can beenhanced, thereby enabling sufficient coating of the titanium hydroxideonto the selenium red. In addition, since the photovoltaic film materialincludes the lithium particles, the presence of the lithium particlesenables maintenance of an electromotive force even under alight-shielded condition.

Meanwhile, the respective embodiments have been described as using thelight-yellow aqueous solution—having been synthesized by means ofaddition of aqueous hydrogen peroxide into titanium hydroxide (Ti(OH)₄)gel—whose concentration is 2%; however, the concentration may be higheror lower than this. In addition, in the description a spray gun isemployed for coating operation; however, another method may be adopted.In addition, as the conductive glass plate, a type which employs an ITOfilm is used; however, another type of a conductive glass plate may beadopted. In the above description, a photovoltaic film is to be formedon a conductive film—which is disposed on a conductive glass plate andwhich serves as an electrode—however, the photovoltaic film may beformed on another type of a conductive membrane, such as a conductivefilm.

Meanwhile, the respective embodiments have been described with use of,as examples of a binder for producing a paste-like photovoltaic filmmaterial, those described above; however, another type of a binder maybe adopted.

In addition, the respective embodiments have been provided on theassumption that a baking operation in the baking step is performed in aninert atmosphere; however, no limitation is imposed thereon, and thebaking operation may be performed in, e.g., an oxidizing atmosphere.

In addition, a lithium chloride aqueous solution is added in preparationof the photocatalyst-coated particles in the first to third embodiments;however, this addition may be omitted. In such a case, the photovoltaicfilm material includes no lithium particles.

Meanwhile, in the descriptions of the respective embodiments, thephotovoltaic film material is paste-like; however, the photovoltaic filmmaterial is not limited to being paste-like, and an essentialrequirement is to be coating-fluid-like. More specifically, thephotovoltaic film material does not necessarily have high viscosity, solong as it has characteristics of coating-fluid. In relation to theabove, the expression “being coating-fluid-like” encompasses a state ofhaving viscosity to a degree which allows coating, which encompasses apaste-like state. In addition, in the above descriptions, mean particlesizes, specific gravities, and the like, of the respective particleshave been defined; however, no limitation is imposed on the definedmeans particle sizes, specific gravities, and the like.

INDUSTRIAL APPLICABILITY

A photovoltaic film material, a method for manufacturing a photovoltaicfilm material, and a method for manufacturing a photovoltaic filmaccording to the invention are suitable for use in a photovoltaic filmemployed in a solar cell. In addition, a photovoltaic film material, amethod for manufacturing solar cell and a photovoltaic film material,and a method for manufacturing a photovoltaic film according to theinvention are suitable for use in a solar cell to be used in alight-shielded condition.

1. A photovoltaic film material for use in a photovoltaic film to bedisposed in a solar cell, comprising photocatalyst-coated particlesincluding: inorganic material particles which are particles of aninorganic material; photocatalyst particles which are coated on thesurface of said inorganic material particles; and lithium particlesattached onto said inorganic material particles and/or saidphotocatalyst particles.
 2. The photovoltaic film material defined inclaim 1, wherein said photocatalyst-coated particles are obtained bymeans of: producing a mixture in which an aqueous solution obtained bymeans of mixing titanium hydroxide gel and aqueous hydrogen peroxide,powder consisting of said inorganic material particles, and water aremixed; leaving to stand a second mixture obtained by means of mixingsaid mixture, and lithium chloride or a lithium chloride aqueoussolution, thereby forming a product material in which titanium hydroxideis coated on at least the surface of said inorganic material particles;and baking said product material.
 3. The photovoltaic film materialdefined in claim 1, wherein said inorganic material which constitutessaid inorganic material particles is an inorganic pigment or a metaloxide.
 4. The photovoltaic film material defined in claim 1, whereinsaid photocatalyst particles are titanium dioxide particles.
 5. Thephotovoltaic film material defined in claim 1, further comprising abinder, wherein said photovoltaic film material is formed into a coatingfluid.
 6. The photovoltaic film material defined in claim 1, whereinsaid binder is any one of: an aqueous solution obtained by means ofmixing titanium hydroxide gel and aqueous hydrogen peroxide; a mixtureof an aqueous solution obtained by means of mixing titanium hydroxidegel and aqueous hydrogen peroxide, and a lithium silicate aqueoussolution; and lithium silicate.
 7. A solar cell including a photovoltaicfilm, wherein said photovoltaic film has photocatalyst-coated particlesincluding: inorganic material particles which are particles of aninorganic material; photocatalyst particles which are coated on thesurface of said inorganic material particles; and lithium particlesattached onto said inorganic material particles and/or saidphotocatalyst particles.
 8. The solar cell defined in claim 7, whereinsaid photocatalyst-coated particles are obtained by means of: producinga mixture in which an aqueous solution obtained by means of mixingtitanium hydroxide gel and aqueous hydrogen peroxide, powder consistingof said inorganic material particles, and water are mixed; leaving tostand a second mixture obtained by means of mixing said mixture, andlithium chloride or a lithium chloride aqueous solution, thereby forminga product material in which titanium hydroxide is coated on at least thesurface of said inorganic material particles; and baking said productmaterial.
 9. The solar cell defined in claim 7, wherein saidphotovoltaic film further comprises titanium dioxide which has beentransformed from titanium hydroxide by means of baking acoating-fluid-like product material obtained by means of kneading saidphotocatalyst-coated particles into an aqueous solution having beenobtained by means of mixing titanium hydroxide gel and aqueous hydrogenperoxide.
 10. The solar cell defined in claim 7, wherein said inorganicmaterial which constitutes said inorganic material particles is aninorganic pigment or a metal oxide.
 11. The solar cell defined in claim7, wherein said photovoltaic film further comprises a binder.
 12. Thesolar cell defined in claim 11, wherein said binder is any one of: anaqueous solution obtained by means of mixing titanium hydroxide gel andaqueous hydrogen peroxide; a mixture of an aqueous solution obtained bymeans of mixing titanium hydroxide gel and aqueous hydrogen peroxide,and a lithium silicate aqueous solution; and lithium silicate.
 13. Amethod for manufacturing a photovoltaic film material for use in aphotovoltaic film to be disposed in a solar cell, comprising: afirst-mixture preparation step of producing a first mixture in which anaqueous solution obtained by means of mixing titanium hydroxide gel andaqueous hydrogen peroxide, powder consisting of inorganic materialparticles, which are particles of an inorganic material, and water aremixed; a second-mixture preparation step of producing a second mixtureby means of mixing lithium chloride or a lithium chloride aqueoussolution into said mixture produced in said first-mixture preparationstep; a production-material formation step of leaving to stand saidsecond mixture produced in said second-mixture preparation step, therebyforming a product material in which titanium hydroxide is coated on atleast the surface of said inorganic material particles; and a bakingstep of baking said product material formed in said product-materialformation step, thereby producing a photovoltaic film material.
 14. Amethod for manufacturing a photovoltaic film material for use in aphotovoltaic film to be disposed in a solar cell, comprising: aproduction-material formation step of producing an aqueous solutionhaving titanium hydroxide, powder consisting of inorganic materialparticles which are particles of an inorganic material, and lithiumchloride, and leaving to stand the aqueous solution, thereby forming aprecipitated product material; and a baking step of baking said productmaterial formed in said product-material formation step, therebyproducing a photovoltaic film material.
 15. The method for manufacturinga photovoltaic film material defined in claim 13, wherein said inorganicmaterial which constitutes said inorganic material particles is aninorganic pigment, or a metal, or a metal oxide.
 16. The method formanufacturing a photovoltaic film material defined in claim 13, furthercomprising a coating-fluid-like-material production step of producing acoating-fluid-like photovoltaic film material by means of mixing saidphotovoltaic film material into an aqueous solution obtained by means ofmixing titanium hydroxide gel and aqueous hydrogen peroxide.
 17. Themethod for manufacturing a photovoltaic film material defined in claim13, further comprising a coating-fluid-like-material production step ofproducing a coating-fluid-like photovoltaic film material by means ofmixing said photovoltaic film material into a lithium silicate aqueoussolution.
 18. The method for manufacturing a photovoltaic film materialdefined in claim 13, further comprising a coating-fluid-like-materialproduction step of producing a coating-fluid-like photovoltaic filmmaterial by means of mixing said photovoltaic film material into amixture constituted of an aqueous solution obtained by means of mixingtitanium hydroxide gel and aqueous hydrogen peroxide, and lithiumsilicate.
 19. A method for manufacturing a photovoltaic film to bedisposed on a solar cell, comprising: a coating step of coating aphotovoltaic film material manufactured in accordance with said methodfor manufacturing a photovoltaic film material defined in claim 16 ontoa conductive film serving as an electrode; and a baking step of baking aphotovoltaic film material having been coated in said coating step. 20.A method for manufacturing a photovoltaic film to be disposed on a solarcell, comprising a coating step of coating a photovoltaic film materialmanufactured in accordance with said method for manufacturing aphotovoltaic film material defined in claim 16 onto a conductive filmserving as an electrode.
 21. The method for manufacturing a photovoltaicfilm material defined in claim 14, wherein said inorganic material whichconstitutes said inorganic material particles is an inorganic pigment,or a metal, or a metal oxide.
 22. The method for manufacturing aphotovoltaic film material defined in claim 14, further comprising acoating-fluid-like-material production step of producing acoating-fluid-like photovoltaic film material by means of mixing saidphotovoltaic film material into an aqueous solution obtained by means ofmixing titanium hydroxide gel and aqueous hydrogen peroxide.
 23. Themethod for manufacturing a photovoltaic film material defined in claim14, further comprising a coating-fluid-like-material production step ofproducing a coating-fluid-like photovoltaic film material by means ofmixing said photovoltaic film material into a lithium silicate aqueoussolution.
 24. The method for manufacturing a photovoltaic film materialdefined in claim 14, further comprising a coating-fluid-like-materialproduction step of producing a coating-fluid-like photovoltaic filmmaterial by means of mixing said photovoltaic film material into amixture constituted of an aqueous solution obtained by means of mixingtitanium hydroxide gel and aqueous hydrogen peroxide, and lithiumsilicate.
 25. A method for manufacturing a photovoltaic film to bedisposed on a solar cell, comprising: a coating step of coating aphotovoltaic film material manufactured in accordance with said methodfor manufacturing a photovoltaic film material defined in claim 17 ontoa conductive film serving as an electrode; and a baking step of baking aphotovoltaic film material having been coated in said coating step. 26.A method for manufacturing a photovoltaic film to be disposed on a solarcell, comprising: a coating step of coating a photovoltaic film materialmanufactured in accordance with said method for manufacturing aphotovoltaic film material defined in claim 18 onto a conductive filmserving as an electrode; and a baking step of baking a photovoltaic filmmaterial having been coated in said coating step.
 27. A method formanufacturing a photovoltaic film to be disposed on a solar cell,comprising: a coating step of coating a photovoltaic film materialmanufactured in accordance with said method for manufacturing aphotovoltaic film material defined in claim 22 onto a conductive filmserving as an electrode; and a baking step of baking a photovoltaic filmmaterial having been coated in said coating step.
 28. A method formanufacturing a photovoltaic film to be disposed on a solar cell,comprising: a coating step of coating a photovoltaic film materialmanufactured in accordance with said method for manufacturing aphotovoltaic film material defined in claim 23 onto a conductive filmserving as an electrode; and a baking step of baking a photovoltaic filmmaterial having been coated in said coating step.
 29. A method formanufacturing a photovoltaic film to be disposed on a solar cell,comprising: a coating step of coating a photovoltaic film materialmanufactured in accordance with said method for manufacturing aphotovoltaic film material defined in claim 24 onto a conductive filmserving as an electrode; and a baking step of baking a photovoltaic filmmaterial having been coated in said coating step.
 30. A method formanufacturing a photovoltaic film to be disposed on a solar cell,comprising a coating step of coating a photovoltaic film materialmanufactured in accordance with said method for manufacturing aphotovoltaic film material defined in claim 17 onto a conductive filmserving as an electrode.
 31. A method for manufacturing a photovoltaicfilm to be disposed on a solar cell, comprising a coating step ofcoating a photovoltaic film material manufactured in accordance withsaid method for manufacturing a photovoltaic film material defined inclaim 18 onto a conductive film serving as an electrode.
 32. A methodfor manufacturing a photovoltaic film to be disposed on a solar cell,comprising a coating step of coating a photovoltaic film materialmanufactured in accordance with said method for manufacturing aphotovoltaic film material defined in claim 22 onto a conductive filmserving as an electrode.
 33. A method for manufacturing a photovoltaicfilm to be disposed on a solar cell, comprising a coating step ofcoating a photovoltaic film material manufactured in accordance withsaid method for manufacturing a photovoltaic film material defined inclaim 23 onto a conductive film serving as an electrode.
 34. A methodfor manufacturing a photovoltaic film to be disposed on a solar cell,comprising a coating step of coating a photovoltaic film materialmanufactured in accordance with said method for manufacturing aphotovoltaic film material defined in claim 24 onto a conductive filmserving as an electrode.